Processes of treating petroleum oils



Patented July 7, 1936 UNITED STATES PATENT OFFICE 2,046,951 PROCESSES OETlgllillgllNG PETROLEUM I No Drawing. Application March 14, 1933,

Serial No. 660,768 r 20 Claims. (Cl. 196-13) This invention relates toprocesses of treating petroleum oils; and it comprises a method ofimproving petroleum products, and particularly lubricating oils orlubricating stocks, wherein the oil or stock is extracted with certainalkyl esters of hydroxy acids, such as lactic acid and glycollicacid,.and having convenient boiling points around or above 300 F; theoil or stock and the extract being afterward gravitationally separatedand solvent ester removed from each; all as more fully hereinafter setforth and as claimed.

Petroleum oils and products are ordinarily mixtures of hydrocarboncomponents differing in solubility in, or miscibility with,various'solvents; and particularly with solvents containing oxygen as apart of the molecule. Such solvents are rarely indefinitely misciblewith petroleum hydr carbons. In a general way, the miscibility orsolubility of highly unsaturated, of highly naphthenic and of aromaticconstituents of petroleum is greater than that of constituents havingmore of a parafiin nature; a fact utilized in the well known process ofpurifying oils with liquid S02.

This differential solvent power has been utilized in different ways andfor different purposes in the art; notably in the S02 process mentioned;in separating more oily from less oily components of slack wax; inseparating unsaturated and aromatic constituents from burning oils andin extracting the more naphthenic components of lubricating oils.Sometimes, the oil, etc. is simply thinned with the solvent; sometimes,itis washed with successive small portions of solvent and sometimes, amixture of oil and solvent is heated to a temperature at whichmiscibility results; the resultant solution beingthen cooled to cause aseparation. In any way of operating, there result two layers of liquidcontaining the two components. These layers are physically separated,that is, are drawn off separately, and are each treated torecover thesolvents; usually, by fractional distillation. Solvent occurs inbothlayers.

The present invention provides solvent liquids which are useful forsomewhat similar purposes, and these liquids exhibit wide diiferences intheir miscibility with various different chemical constituents ofpetroleum oil; small difierences in chemical composition of theseconstituents being accompanied by wide differences in miscibility Theseliquids also have a convenient variation of miscibility withtemperature, and allow the pro-' duction of hot homogeneous mixtureswhich separate on cooling. Their specific gravity is higher than that ofpetroleum oils and this quality permits formation and separation ofunder layers containing a considerable amount of dissolved oil; Theyare,'further,- of a convenient boiling point, ranging between 300 and400 F., thereby rendering their removal from an oil mixture easy and arebut little affected by water or steam. Since the solvent is usuallyremoved from the separated oil fractions by volatilization(distillation) this stability is advantageous. Withinthe boiling rangementioned (300-400 F.) removal of solvent from the extracted oil can beeiiected, even at atmospheric pressure, withoutcracking or injuring thelubricating oil.

These liquids are the various alkyl esters of certain hydroxy acids;organic acids which, like lactic and glycollicacids, have an alcoholgroup in the molecule. They contain oxygen inseveral forms, as carbonyland as hydroxyl, as well as the esterifying' oxygen atom. Theirconvenient properties as differential solvents are possibly due to thismolecular structure. Among the esters which have been used and have beenfound particularly suitable are the organic alkyl esters of hydroxycompounds of the lower membered fatty acids. Examples of these estersare isopropyl lactate, ethyl lactate and other lactic acid esters ofhydroxy compounds which function as alcohols. Isopropyl glycollate isanother useful ester. Ethyl lactate boils at 310 F., n-propyl lactate at370, isopropyl lactate at 330 and normal butyl lactate at 371. None ofthese esters is corrosive, poisonous, irritating or readily inflammable. Triethyl citrate has shown itself of value.

All these esters exhibit a wide differential'in miscibility withconstituents of petroleum oil and all have a convenient boiling point,so that they may be. readily removed after use. While they may be usedin the other operations stated ante, they will be described here moreparticularly in their use in improving lubricating oils and lubricatingoil stocks.

Minerallubricating oils are characterized by an undesirably greatvariation of viscosity with temperature. This is particularly true ofmineral lubricating oils produced from crude oils of naphtheniceriginand such oils are far from ideal for use where extremes of temperature,are encountered. For example, atypical naphthenic lubricating oil havingsuitable viscosity for use in automobile engines at operatingtemperature is muchtoo stifi for use at the starting temperaturesfrequently encountered in winter time. Such an oil, on extraction withisopropyl lactate, gives a lubricating oil with much bettertemperatureviscosity relationships.

Each of the esters mentioned is completely miscible while hot with anequal volume of lubricating oil; the temperature required for completemiscibility being highest for ethyl lactate and lowest for butyllactate. Each one of them can be used for making a mixture withlubricating oil at a high temperature which will separate into twolayers at a lower temperature; and the heavier (underlying) layer willcontain, predominately, the more naphthenic constituents of thelubricating oil, while the upper and lighter layer is a lubricating oilcontaining some solvent andv proportionately freed of the undesirablenaphthenic constituents. The miscibility temperature and theseparationtemperature with each ester differ for different oil stocksand lubricating oils, being higher in general for mid-continent stocksthan for coastal stocks. The particular ester most suitable varies tosome extent with the stock; but for general purposes, isopropyl lactateis regarded as particularly advantageous.

Instead of heating to the miscibility temperature and then cooling tothe separation temperature, it is possible to directly wash the oil withthe solvent at temperatures within the separation range. Successivesmall portions of solvent may be used; and occasionally with greateradvantage countercurrent washing in appropriate apparatus is possible,because of the differences in specific gravity between solvent and oil.However, the described operation of producing a homogeneous, orsubstantially homogeneous, solution of oil and ester at elevatedtemperatures, followed by cooling and consequent separation is generallythe more advantageous. Simpler apparatus suffices for this operation andless labor is required.

The typical mode of operation when using the heating and coolingoperation is as follows. .A lubricating oil or lubricating stock, as thecase may be, is mixed with about its own volume of the solvent and themixture is heated, while being stirred, until a homogeneous, orsubstantially homogeneous, liquid is produced. Ordinarily, heating is toa temperature a few degrees above that required for miscibility, as thisquickens the operation. The mixture is then allowed to cool while beinggently stirred. Cooling is continued down to a point below that at whichseparation of the two phases begins to take place. This is generally 30to 50 Fahrenheit below the miscibility temperature. Stirring is thendiscontinued. Separation occurs, and two layers result; the uppercontaining a. purified oil and some solvent, and the lower comprisingsolvent and the extracted components of the oil undergoing treatment.The lower layer will contain the bulk of the solve'nt. The two layersare mechanically separated in any of the ordinary ways, as by drawingoff the lower layer, and the liquid of each layer is then treated torecover the solventthis being ordinarily done by distillation.

The solvent may be removed from the extracted fractions by ordinary firedistillation, or

by filming the oil and solvent mixture to form an extended surface, andevaporating under reduced pressure.' Distillation in a fractionatingcolumn with the aid of a partial vacuum (approximately 30 to 50 mm.) isadvantageous, as good separation is readily obtained. If batchdistillation be effected at atmospheric pressure, in finishing thedistillation the undistilled "oil may rise to excessively hightemperatures before the last of the solvent is removed. 'Hence, reducedpressure is advantageous. Steam distillation can be used, but is notparticularly desirable.

Alternatively, the bulk of the solvent or its last aceaoci traces can beextracted from the oil by water. The water extract, on distillation,gives an azeotropic mixture distilling over before the solvent itselfdistils, which, in the case of isopropyl lactate, representsapproximately two parts of water and one part of lactate, and has avapor temperature on distillation of 207.5 F. The solvent may be washedout of the treated oil by use of a condensate of this 2:1 mixture. Thewash liquid on distillation will yield again the azeotropic mixture,leaving dry esters behind. Because of its low boiling point, anyresidual washing liquid left in the oil is readily removed by commonmeans.

When solvent is removed from the oil by distillation in presence ofsteam there is apt to be some hydrolysis of the ester, and some of theesters are more easily hydrolyzed than others. They are all, however,resistant to the action of water and steam and this resistant property,coupled by the fact that they are more or less miscible with water, isadvantageous in the present invention. Inhibitors, such as lecithin, maybe used to restrain hydrolysis.

In all cases of treating naphthenic lubricating oils or lubricating 011stocks, the treated oil has a better temperature viscosity curve, This,is an advantage of the group of solvents used in the present invention.

The present invention is an additional step in the processes of makingcommercial lubricating oil; and it is to be understood that usualrefining processes may be applied to the oil before and after theoperation of the present invention.

In a specific embodiment of this invention producing a lubricating oilof improved temperatureviscosity characteristics from naphthenic stock,the stock was a naphthenic distillate with a viscosity of 1300 at F. andof '73 at 210 F. The viscosity index was -2 and the specific gravity at60 F. was 0.9345. One volume of this stock was mixed with 1 volume ofisopropyl lactate and heated to F. Complete miscibility occurred at 131F. The mixture was cooled to 95 F. with stirring and the coolingcontinued without stirring to 86 F. Separation occurred and the lowerlayer was drawn off and was found to be composed of 19 per cent oil and81 per cent solvent. The upper layer was composed of 81 per cent oil and19 per cent solvent. The solvent was distilled off from both layersunder 25 mm. mercury absolute pressure. It distilled oil? atapproximately F.

The lubricating oil derived form the upper layer was of improvedquality. It was, however, retreated. To this end, it was mixed with anequal volume of the same solvent and heated to 140 F. Miscibilityoccurred at 135 F. The mixture was cooled to 104 F. with the stirrergoing and further cooled without stirring to 95 F. The lower layer hadthe same composition as the first operation, viz., 19 per cent oil and81 per cent solvent, while the upper layer, like the upper layer of thepreceding treatment, was also 19 per cent solvent and 81 per cent oil.Both layers were treated as before described to remove and recoversolvent.

narily, one or two treatments are considered suf- 70 extraction, 12 percent. The first extraction left 76' aosacsi t2 per cent of the stock inthe oil layer and. the other two extractions reduced this, respectively,to 68 per cent and 56 per cent. It will be noted' that there was. noappreciable change in the solubility in the several extractions. Thefinal product obtained had a viscosity at 100 F. of 1020 and at 210 F.of '71, the viscosity index being '34. The lubricating oil finallyobtained was submitted to the usual acid treatment and alkali wash andclay filtering to produce a commercial oil.

In another specific embodiment, treating a paramnic stock and usingn-butyl lactate, a midcontinent lubricating stock after being subjectedto the usual refining and dewaxing by centrifugal methods was mixed withan equal volume of nbutyl lactate. On'heating, a homogeneous liquid wasformed at 100 F., but heating was continued to 113 F. The mixture wascooled with stirring to 68 F. Stirring was then discontinued and coolingcontinued to 59 F. Separation occurred and the lower layer was drawn offand was found to contain 21 per cent oil and 79 per cent solvent. Theupper layer contained 23 per cent solvent. Both layers were distilled torecover solvent. The upper, or oil layer, was freed of solvent. The oilwas then diluted with half its volume of light naphtha, was washed twicewith a small proportion of water, was freed of naphtha, and then airblown till dry. An 80 per cent yield was obtained.

The viscosity data were as follows:

Viscosity Viscosity Viscosity 100" 210" index Original 870 74 72Finished 780 72 78 per cent solvent, while the lower layer containedabout 82 per cent solvent and 18 per cent naphthenic oil. Thelubricating oil showed a viscosity at 100 F. of 1190 and at 210 F. of72; the viscosity index being 12. The yield of lubricating ofl,calculated back tolubricating stock, was per cent.

In the three foregoing examples, solvent and oil were used in aboutequal volumes. Sometimes, other ratios are desirable. In a typicaloperation, 2 volumes of isopropyl lactate were used for 1 volume of thecoastal oil used in the first and third previous examples. With theseproportions, the temperature of complete miscibility was 135 F. and thetemperature was dropped to F., at which temperature there was clearseparation into two layers. The upper layer contained 80 per cent ofoil, while the lower layer contained about 18 per cent of extractfrom'theoil. The total yield of lubricating oil was 53.5 per cent of thestock and it had the following characteristics:

Viscosity Viscosi Viscosit 210 ty index y Original. 'Undissolvcd oil.Dissolved oil While the process has been specifically dewlth anotherportion of the said liquid ester.

scribed in its application to lubricating oil only, it can be used inseparating any pair of proximate constituents of an oil having differingsolubility.

In a specific embodiment of the present invention using countercurrentcontact, a slow cur- 5 rent of isopropyl lactate at a temperature around95 F. was allowed to pass downward through a packed tower of the type ofascrubbing tower. A slow current of the same coastal oil mentioned antewas sent upward through the tower from a point somewhat above its base,the eflluent oil at the top being removed at a point somewhat above thepoint of introduction of isopropyl lac tate. The rates of flow werecontrolled to give a. ratio of solvent to oil of between 1:1 and 2:1. nThe so-scrubbedoil was treated to recover the solvent and solvent wasalso recovered from the charged solution passing out at the base. Theresults obtained were like those obtained in the detailed examples givenante.

The methods of the present invention can be usefully employed onfinished lubricating oil, as well as on lubricating 011 stocks. 4

While gravitational separation of the two phases of the liquid has beenmore particularly described, 25 like results can be obtainedcontinuously and more quickly by the use of a centrifuge, the liquidsupplied being a mixture of oil and solvent which has been agitated soas to come to solution equilibrium and is at the proper tempera- 30 turefor clear separation.

Removal of residual solvent by the use of water or recycled distillatefrom the azeotropic distillation is sometimes advantageous as avoidingthe heating of the oil incident to recovery by 35 distillation. Thewater extracts are readily separated by azeotropic distillation intofractions, one of which is prcdominatingly aqueous and the other ispredominatinglyester. Either fraction may be recycled in the process.The aqueous fraction is particularly well adapted for washing the oil toget out the. ester solvent.

What we claim is: V

1. The process of separating and recovering proximate constituents ofpetroleum products which comprises intimately contacting a petroleumproduct in liquid form 'with a stable liquid alkyl ester of an organichydroxy acid, said ester having a boiling point not over 400 F., undercircumstances permitting development of a twophase liquid and separatingthe two phases by gravity.

2. The process of claim 1 wherein contact is effected at a temperaturehigh enough to produce homogeneous solution of the two liquids and thetemperature is then lowered to develop a twophase liquid.

3. The process of claim 1 wherein contacting is effected between flowingbodies of the two liquids'.

4. The process of claim 1 wherein the petroleum product is a lubricatingoil stock containing naphthenic constituents.

5. The process of claim 1 wherein the petroleum product and the esterare contacted in sub-' stantially equal proportions.

6. The process of claim 1 wherein the described operation is repeated,the petroleum product once extracted with liquid ester being againextracted .7. The process of claim 1 wherein the two liquid phasesdeveloped are allowed to stratify under ravitation.

8. The process of separating and recovering 75 proximate constituents ofpetroleum products which comprises intimately contacting such a productwith isopropyl lactate, permitting the development of a two-phase liquidand separating the two phases.

9.-The process of separating and recovering proximate constituents oipetroleum products which conprises intimately contacting such a productwith isopropyl glycollate, permitting the development of a two-phaseliquid and separating the two phases.

10. The process of separating and recovering proximate constituents ofpetroleum products which comprises intimately contacting such a productwith butyl lactate, permitting the development of a two-phase liquid andseparating the two phases.

11. The process of separating and recovering proximate constituents ofpetroleum products which comprises intimately contacting such a productwith a liquid ester oi an organic hydroxy acid selected from a groupconsisting of isopropyl lactate, ethyl lactate, n-propyi lactate,triethyl citrate, isopropyi glycollate and butyl lactate, permitting thedevelopment of a two-phase liquid and separating the two phases.

12. The process of separating and recovering proximate constituents ofpetroleum products which comprises intimately contacting such a productwith a stable liquid organic alkyl ester of a hydroxylated low memberedfatty acid. said ester having a boiling point not over 400 F.,permitting the development of a two-phase liquid and separating the twophases by gravity.

13. The process of claim 12 wherein contact is eiiected at a temperaturehigh enough to produce homogeneous solution of the two liquids and thetemperature is lowered to develop a two-phase liquid.

14. The process oi. claim 12 wherein contacting is eflfected betweenflowing bodies of the two liquids. 5

15. The process 01' claim 12 wherein the petroleum product isa'iubricating oil stock containing naphthenic constituents.

16. The process 0! claim 12 wherein the petroleum product and the allrylester are contacted in substantially equal proportions.

17. The process of claim 12 wherein the described operation is repeated,the petroleum product once extracted with liquid alkyl ester being againextracted with another portion of the said 15 liquid ester.

18. The process of claim 12 wherein the two liquid phases developed areallowed to stratify under gravitation.

19. The process of separating and recovering proximate constituents ofpetroleum products which comprises intimately contacting a petroleumproduct in liquid form with a stable liquid aikyl ester of an o ganichydroxy acid, said ester having a boiling point not over 400 F., undercircumstances permitting development of a two-phase liquid, separatingthe two phases by gravity, washing the liquid of the lighter phase witha liquid comprising water, distilling the washings under azeotropicconditions to obtain a 3C distillate and a residue as more and lessaqueous fractions and recycling one of such fractions.

20. The process of claim 19 wherein the more aqueous fraction isrecycled for washing purposes.

ERIC B. HJERPE. WILLIAM A. GRUSE.

